Microwave drying apparatus

ABSTRACT

A device is provided for drying a continuous web or sheet of material passing through a drying zone. The device includes two air cushions which face each other and force the sheet of material passing through the drying zone to stay midway between opposite microwave drying units. Further, to prevent wrinkling of the sheet material, the air cushions are provided by spaced slots extending at an angle to the path of travel of the sheet to ensure that streaking of a coating on the sheet is obviated.

[4 1 June 27, 1972 United States Patent Stephansen [54] MICROWAVEDRYINGAPPARATUS 3,324,570 6/1967Flaithetal,..............................34/l$6 [72] Inventor:Erik,stephammpostercimcam 3,181,250 5/1965Vits......................................34/l56X Bechtel InternationalCorporation Primary Examiner-Carroll B. Dority, Jr. Attorney-Eckhoff andl-loppe [73] Assignee:

[22] Filed:

[21] Appl. No.: 85,568 ABSTRACT A device is provided for drying acontinuous web or sheet of 521u.s.c1..........................................34/1,34/156, 34/160material Passing 8 a drying The device includes two air cushions whichface each other and force the sheet of material passing through thedrying zone to stay midway [51] Int.

5s Fieldorsemi..........................................

/ between opposite microwave drying units. Further, to prevent wrinklingof the sheet material, the air cushions are provided R i l! e C ed byspaced slots extending at an angle to the path of travel of the sheet toensure that streaking of a coating on the sheet is obviated.

UNITED STATES PATENTS 3,491,457 1/1970 Schrelber et a1 .34/1 3,449,8366/1969 Schreiber et 6 Claims, 4 Drawing Figures PATENTEDJURZY 1912 saw 1INVENTOR.

ATTORNEYS PATENTEDJunN 12m sum 2 or 2 DUMMY LOAD BYEIZIK W. 5 73mmiawnfi 4; 1%

GENEKATOR ATTORNEYS MICROWAVE DRYING APPARATUS BACKGROUND OF THEINVENTION The simultaneous application of a gas to a sheet of materialundergoing drying by microwave energy is known and one can refer toprior US. Pat. Nos. 3,449,836, 3,475,827 and 3,491,457. In these andother prior art devices, however, the gas impingement was such that gaswas not effective to maintain the web spaced equally between theopposite waveguides providing the microwave energy application.

SUMMARY OF THE INVENTION It is in general the broad object of thepresent invention to provide an improved drier for a continuous web ofmaterial by microwave energy in which opposite and equal air cushionsare provided on opposite sides of the web to hold the web in acentralized position as it passes through the opposite waveguides of themicrowave drier.

A further object of the present invention is to provide air cushions sospaced and provided that wrinkling of the web or of a coating on the webis obviated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of anembodiment of the apparatus for practicing the present invention.

FIG. 2 is a section taken transversely through the means providing theopposite air cushions.

FIG. 3 is a perspective view showing the air outlet means provided at anangle to the run of the web.

FIG. 4 is a top plan view of one-half of the microwave drier assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the description whichfollows, it is assumed that a coated or a partially dry web is beingdried by the combined action of microwave energy and jets of a dryinggas such as air, nitrogen or superheated steam applied to a web of thesheet material indicated at 10. The web is drawn through the drier bymeans well known to those skilled in the art and therefore is notillustrated. The movement of the web can be in the direction indicatedby the arrow or in the opposite direction.

The drier comprises upper and lower sections indicated at 11 and 12.These sections are alike so a description of one will suffice. The driersections 11 and 12 are spaced apart about a quarter of an inch tominimize the tendency for dust or lint which may accumulate between thetwo halves to cause arcing. Each drier section includes a plurality ofwaveguides and a plurality of gas distribution means and gas collectionmeans. Basically, each drier section includes opposite parallel endwalls 13 and 14 joined together by walls 16 and 17 which provide a firstduct through which the drying gas is passed for release against the web.A wall 18 also extends from end wall 14 toward the opposite end wall 13but is spaced therefrom. A wall 19 extends from the end wall 13 towardthe end wall 14 but is also spaced therefrom. Extending from wall 14 areparallel walls 21 and 22 which extend toward end wall 13, the end ofthese walls being closed as at 23 and by a top plate 24 provided with aplurality of apertures 26 through which the drying gas is exhausted.Angular guide plates 27 are provided at the junction of each of theaforementioned walls with an end wall to direct the flow of themicrowaves through the drier.

A source 31 of microwave energy is provided to feed the spacedwaveguides through line 32 into the waveguide provided by walls 17 and18. The generator 31 can be any-wellknown source of RF energy and in onepractical embodiment of the invention the energy source consisted of aKlystron and associated power supply operating at 2,450 mI-Iz. Suitablythe RF generator operates at a frequency from about 300 to 30,000 mI-Iz.Thus the ISM allocated frequencies of 915; 2,450; 5,800 and 22,125 mI-Izare suitable.

The microwave energy is fed into the waveguides provided sequentially,for example, by walls 17 and 18, I8 and l9, l9 and 21, 22 and 19, 19 and18, and 18 and 16 to pass through the drying section. At the terminalend 33 of the waveguide a dummy load 34 is provided to absorb excessenergy and, in case of a web break, to absorb total energy input. Themicrowave energy is introduced through a split microwave tee, one halfbeing on the upper section 11 and the other half being on the lowersection 12. The usual microwave tuning devices are included and sincethese are well known they are neither described nor shown.

In accordance with the present invention, there is provided inconjunction with and between walls 16 and 17 (FIGS. 2 and 3) an airdistribution device, generally indicated at 36, which includes a base 37having an upstanding flange 38 provided centrally thereof and providinga support for a cover 39 which fits in spaced relation between walls 16and 17 and in the plane of the upper ends of the walls and fitting closeto the edges of the walls so that air can escape between the cover andthe walls, as is shown in FIG. 2, and through slots 41 provided in thecover 39.

As appears in FIG. 2, the air release occurs on opposite sides of thesheet and under conditions such that the forces applied by the oppositeair streams to the sheet are opposite and equal. Further and inaccordance with the preferred embodiment, the slots 41 are at an angleto the run of walls 16 and 17 so that the air is released angularlyacross the sheet. This prevents streaking of any coating which may havebeen applied to the sheet. If the web is not coated or if streaking isnot objectionable, the slots can extend parallel to the run of thesheet. The air is supplied by a fan 46 through a manifold 47 connectedby line 48 to each of the air inlets. If desired, the air may be heatedand filtered. The air is exhausted through outlets 49.

I claim:

1. In an apparatus for drying a moving web of a sheet material moving inone direction through the apparatus, the apparatus including at oppositeedges of the moving web and in spaced relation thereto opposite firstand second end walls extending parallel to said direction, a top walland a bottom wall extending between said end walls generally parallel tothe plane of the web of sheet material and on opposite sides thereof, athird and a fourth wall extending from each said top and bottom walltoward said web of sheet material and between said end walls to providea gas duct, means for supplying gas to said duct for discharging gasagainst said web, a fifth wall extending from said first end wall towardthe second end wall and spaced therefrom to provide a waveguide, a sixthand a seventh wall extending from the first end wall toward the secondend wall to provide a gas exhaust duct and an extension of thewaveguide, and means for feeding microwave energy into said wave guide.

2. In an apparatus for drying a moving web of sheet material as in claim1, an eighth wall extending from the second end wall toward and spacedfrom the first end wall between the fifth and sixth walls to continuethe waveguide with the fifth wall.

3. In an apparatus for drying a moving web of sheet material as in claim2, wherein said sixth and seventh walls are spaced from the second endwall and are closed at their ends adjacent the second end wall, a topplate covering the sixth and seventh walls and having a plurality ofapertures therein through which the gas is exhausted, said sixth walldefining a continuation of the waveguide with the eighth wall.

4. In an apparatus for drying a moving web of sheet material as in claim3, wherein gas distribution means comprising slot means is in said gasdischarge duct between said third and fourth walls to evenly distributegas against said web.

5. In an apparatus for drying a moving web of sheet material as in claim4, wherein said gas distribution means comprises an upstanding flangeextending longitudinally in equally spaced relationship between saidthird and fourth walls, a cover supported on said flange in spacedrelation between the third and fourth walls and in the plane of theupper ends of the third and fourth walls to define longitudinallyextending slots between the opposite edges of the cover and the adjacentedges of the upper ends of the third and fourth walls, a plurality ofslots in said cover disposed at an angle to the direction of 5 movementof said web and at an angle to the third and fourth walls so that gas isreleased angularly across the web of sheet

1. In an apparatus for drying a moving web of a sheet material moving inone direction through the apparatus, the apparatus including at oppositeedges of the moving web and in spaced relation thereto opposite firstand second end walls extending parallel to said direction, a top walland a bottom wall extending between said end walls generally parallel tothe plane of the web of sheet material and on opposite sides thereof, athird and a fourth wall extending from each said top and bottom walltoward said web of sheet material and between said end walls to providea gas duct, means for supplying gas to said duct for discharging gasagainst said web, a fifth wall extending from said first end wall towardthe second end wall and spaced therefrom to provide a waveguide, a sixthand a seventh wall extending from the first end wall toward the secondend wall to provide a gas exhaust duct and an extension of thewaveguide, and means for feeding microwave energy into said wave guide.2. In an apparatus for drying a moving web of sheet material as in claim1, an eighth wall extending from the second end wall toward and spacedfrom the first end wall between the fifth and sixth walls to continuethe waveguide with the fifth wall.
 3. In an apparatus for drying amoving web of sheet material As in claim 2, wherein said sixth andseventh walls are spaced from the second end wall and are closed attheir ends adjacent the second end wall, a top plate covering the sixthand seventh walls and having a plurality of apertures therein throughwhich the gas is exhausted, said sixth wall defining a continuation ofthe waveguide with the eighth wall.
 4. In an apparatus for drying amoving web of sheet material as in claim 3, wherein gas distributionmeans comprising slot means is in said gas discharge duct between saidthird and fourth walls to evenly distribute gas against said web.
 5. Inan apparatus for drying a moving web of sheet material as in claim 4,wherein said gas distribution means comprises an upstanding flangeextending longitudinally in equally spaced relationship between saidthird and fourth walls, a cover supported on said flange in spacedrelation between the third and fourth walls and in the plane of theupper ends of the third and fourth walls to define longitudinallyextending slots between the opposite edges of the cover and the adjacentedges of the upper ends of the third and fourth walls, a plurality ofslots in said cover disposed at an angle to the direction of movement ofsaid web and at an angle to the third and fourth walls so that gas isreleased angularly across the web of sheet material to prevent streakingor wrinkling of said web of sheet material as it is moved through saiddrying apparatus.
 6. In an apparatus for drying a moving web of sheetmaterial as in claim 5, wherein a plurality of gas discharge ducts,waveguides and exhaust ducts are alternately arranged in said dryingapparatus.